“CBD has the ability to bind to receptors in the body that are part of the human cannabinoid system, called endocannabinoids, that can influence pain, itch and mechanisms of inflammation,” Dr. Friedman says. “We know that when CBD binds to the CB2 [cannabinoid receptor type 2] as well as other receptors, it can be involved in not just anti-inflammatory activity, but it can facilitate an array of activities that resolve inflammation. It can stimulate the secretion and recruitment of cells that are important for removing debris and allowing for proper skin maturation and healing.”
While the relationship may be complex, studies that point to practical applications are emerging. A 2016 study showed that an endocannabinoid called anandamide was able to prevent the production of key inflammation signals that are known to initiate and perpetuate psoriasis in skin and immune cells. 
Outcomes from a 2019 study investigating a topical CBD ointment applied to skin lesions twice daily for two months indicated that the CBD ointment improved skin hydration and elasticity as well as quality-of-life measures that were assessed with the Psoriasis Area Severity Index. 
A more recent study published at the end of 2020 examined a shampoo containing CBD that was effective at reducing the severity of scalp inflammation, itching and burning in patients with scalp psoriasis or seborrheic dermatitis. 
Other studies point to a CBD benefit for quality-of-life measures related to psoriasis. There is evidence that CBD may improve sleep and reduce depression and anxiety, but more research is needed to clarify this connection. 
A CBD-derived product currently on the market, Epidiolex, is approved by the Food and Drug Administration (FDA) for the treatment of seizures associated with certain epilepsy syndromes and tuberous sclerosis.  “This means that we have a lot of useful safety information when it comes to systemic administration,” Dr. Friedman says. “However, we have no data specific to psoriasis.”
When it comes to OTC products, oral CBD products are technically not legal because they are not FDA-approved drugs or supplements, Dr. Friedman adds. But discrepancies between federal and state laws have resulted in poor regulation and oversight and continued sales. This also has led to product labels that do not accurately reflect the actual CBD content, Dr. Friedman points out.
Data reported in the Journal of the American Medical Association showed that CBD products varied widely in their concentrations.  Among 84 CBD-containing products sold online in 2016, nearly half (42.85%) were under-labeled, meaning the actual amount of CBD in the product was more than 10% above the labeled concentration. About one-quarter (26.19%) of the products contained at least 10% less CBD than the label noted.
A smaller, more recent study found that only 12% of products were within 20% of what the label noted. Sixty percent of products contained CBD concentrations well below the labeled value, and 8% exceeded the labeled value by 50%.  Additionally, some studies have shown that OTC formulations may carry impurities that can result in allergic contact dermatitis. 
This inconsistency suggests a need for federal and state regulatory agencies to take steps to ensure label accuracy for these consumer products. Right now, you don’t always know what you’re getting when you’re buying OTC CBD products, Dr. Friedman says.
“Now, let's be honest: If there's nothing in there that's harmful, does simply putting a cream on psoriatic skin have benefit? Yes,” he says. “Simply moisturizing the skin, softening that really thick retained stratum corneum [outer layer of the skin], could have some benefit both from a symptom perspective, but even maybe some mild anti-inflammatory activity.”
However, CBD often is combined with other ingredients like camphor, which can relieve pain, irritation or itching, or salicylic acid, which acts to break down thick, scaly skin. So it's hard to know what's actually doing the work, Dr. Friedman says.
Topicals designed to effectively deliver CBD into the skin need to be developed with specific factors in mind, says Dr. Friedman. Cannabinoids are very lipophilic, meaning they like fatty environments. To constitute CBD in an effective topical formulation, the topical has to be greasy or oily – hence, CBD oil. Also, the top layer of the skin is full of fat. When you put a topical ingredient that likes a fatty environment on the skin, it has a hard time penetrating and will remain in that top layer. This is true of cannabinoids. Now, consider psoriasis, in which you have a very thick top layer, and that makes it harder for the cannabinoid to penetrate the skin, Dr. Friedman explains.